In the field of optical communication and optical computing there is a strong demand for optical gates capable of performing very fast execution of logic functions, switching, and processing. Such optical gates may be used for ultra fast information routing and switching along optical communication networks and may be used to manage and process information in optical computing systems.
U.S. Pat. No. 5,144,375, “Sagnac Optical Logic Gate” by M. Christina Gabriel et. al. (Sep. 1, 1992) discloses an invention for optical gate that is based on a Sagnac loop that includes Non linear Element (NLE) that is excited by an optical pump signal to generate a phase shift.
U.S. Pat. No. 5,987,040, “Optical AND Gate” by Derek Nesset et. al (Nov. 16, 1999) discloses an invention for optical AND gate which is based on the principle of Four-wave mixing (FWM) and incorporating a pump signal to generate a dynamic grating.
U.S. Pat. No. 6,005,994, “Optical Switching Gate” by Robert I. MacDonald et. al (Dec. 21, 1999) discloses an invention for optical AND gate which is based on the principle of changing the absorption of a fiber using two pumping lasers.
As discussed below, the use of control pump signals make the optical gates described in the U.S. Pat. Nos. 375, 040, and 994 more expensive, complicated, slower, power consuming and hard to miniaturize.
The use of external control pump signals requires additional light sources, such as, lasers that operate at wavelengths that are different from the wavelength of the information signals. The need for additional lasers makes the devices more expensive and complicated. In addition, the lasers are made from different materials than those used to produce waveguides, thus they can not be integrated on a chip for miniaturization of the gates.
The power that the pumping sources consume is an additional factor that limits the miniaturization of the gates since it requires the use of heat dissipation techniques. The need for external pump control signals also requires an electronic control and synchronization units which further increases the complication and the cost of such gates.
The need to activate the pumping laser and to turn it on from its non-active state (under the lasing threshold) to its lasing mode is a time consuming process. An additional relatively slow process that starts only after the pumping laser is turned on is the process of the excitation of the Non Linear Element (NLE). The excitation of the NLE, using the turned on laser, from its non-excited state to its saturated level, is also a relatively slow process that adds time to the turn on time of the laser.
Another invention is disclosed in Japanese patent JP6167732 by Nakano Masakazu (1994-06-14). The invention discloses synthesizing means that synthesizes the beams inserted to its input and emitting the synthesized beams toward an absorbing plate. The absorbing plate transmits the light only when it is saturated by a high intensity beam. While patent 732 does not require external control signals, it still suffers from the following drawbacks:
In order for the gate to produce a beam with an intensity that can saturate the absorbing plate, the input beams should have very high intensity (greater than 65 KW). Such high intensity is not practical for many applications used in communication networks and computing systems.
The turn on of the gate to produce a “1” logic state requires the transition of the absorbing plate from ground state to a saturated level. Such a transition is relatively slow and the recovery time from saturated state to ground state might be even longer.
Thus the gate, described in patent 732 is relatively slow and is suitable only for application in which the beams are of very high intensity.
Accordingly, it is an object of this invention to provide optical logic gates such as optical logic AND and NAND gates that are activated by the information signals and do not require the use of external control signals.
It is another object of this invention to provide optical logical gates which are capable of being operated in the range of intensities used in optical communication networks and computing systems.
Still it is an object of this invention to provide fast optical logical gates that their speed is limited only by the recovery time of fast NLE's.